Long Island Democratic Assemblyman Todd Kaminsky announced Sunday that he’s running to fill the seat left vacant by disgraced former state Senate Majority Leader Dean Skelos, a Republican.

“There is a real cost to corruption,” Kaminsky said. “We are at a pivotal moment for Long Island and for New York. If we don’t fix what’s wrong with our government, we will not be able to fix what’s wrong with our cities, villages and towns. Today is when we start.”

Kaminsky, a former federal prosecutor who represents Long Island’s South Shore, immediately picked up an endorsement from Gov. Cuomo, who praised him for “fighting every day to support Long Island’s working-class families.”

Skelos’ Ninth Senate District seat opened in December when he was convicted on charges of bribery, extortion and conspiracy.

Kaminsky’s announcement has been expected for most of January. He got the nod to run for the seat from the Nassau County Democrats on Jan. 5. And a campaign committee that opened around the same time has raised more than $250,000 for him.

Kaminsky was elected to the state Assembly in 2014 after serving in the Public Integrity Section in the federal prosecutor’s office covering Brooklyn, Queens and Long Island.